High pressure wire reinforced hydraulic hose is typically used on a variety of machines, including earthworking machines, to provide a flexible connection between several moving parts of a common hydraulic circuit employed on or with the machine. Most often, such hoses are employed in circuits and articulated machines or machines wherein one part must move relative to the other part. Typical reinforced hydraulic hose structures utilized in such applications are illustrated in U.S. Pat. No. 2,128,814 issued to Gish; U.S. Pat. No. 3,312,528 issued to Haas; U.S. Pat. No. 3,357,456 issued to Grawey et al; and U.S. Pat. No. 3,866,633 issued to Taylor.
All of the hose structures described in the aforementioned patents include a hollow elastomer core on which successive cylindrical plies of wire reinforcing are concentrically applied to contain the radial and axial pressures developed within the hose when it is placed in service at high pressures in the range of 3,000 psi or greater. To some extent, the burst strength of these hoses can be increased by adding additional reinforcing plies (within limits) and in most cases, an even number of reinforcing plies must be used so that the angular wrap of opposite hand of two adjacent plies balance one another.
One of the critical areas of construction of such hydraulic hose is the core structure. With the exception of the aforementioned Grawey at al U.S. Pat. No. 3,357,456, the core structures in such hoses have been typically extruded as a cylindrical tube to obtain a continuous circular wall for the hose and to provide the foundation upon which the wire reinforcing can be applied to complete the hose. Typically, the core is protected with a layer of fabrics as mentioned in the above patents, before the reinforcing is applied.
The above Grawey et al patent, teaches the preparation of an improved core in such wherein a laminated tape composed of two layers of elastomer and one layer of fabric sandwiched therebetween is wrapped on a mandrel, usually in a helical overlapping relationship, to form a core. This combination elastomer and fabric core generally has a greater capacity to restrict the embedding or "biting" of the reinforcing wires into the core structure, and therefore helps achieve greater concentricity of the first ply of cylindrical reinforcing wrapped on the core structure. Since each cylindrical reinforcing ply forms the base for the subsequent cylindrical reinforcing ply, an overall improvement in hose structure is thus achieved. U.S. Pat. No. 3,866,633 attempts to appropriate the teachings of the Grawey et al patent by an extruded core structure which utilizes aligned fibers in an extruded cylindrical core.
One of the objects of the present invention is the provision of a stiffer "base" on which to wrap the first ply of wire, which improves the wire lay in this ply. With improved wire lay in this play and subsequent plies, stress distribution during hose preparation should be more uniform between the wires in each individual ply, resulting in a higher burst pressure approaching the theoretical.
Still another object of the instant invention is to provide a hydraulic hose with an improved laminated core structure wherein improved "knit lines" are achieved in a helically wrapped tape forming the core.
In addition, an object of the instant invention through the utilization of a two-layered tape, is to eliminate some of the partial cure that results in multi-layered tapes as a result of viscous shear in the rubber, which causes localized heat buildup and partial cure of the heat sensitive compounds therein.